feat: env-defined endpoint aliases (http-capable, local Ollama friendly)

majordomo's built-in LLM_* env DSNs are HTTPS-only (DSN.BaseURL forces https),
so they can't express a plaintext local Ollama. Add Gadfly-native env families
that register named providers/aliases with majordomo before resolution:

  GADFLY_ENDPOINT_<NAME>="<provider>|<base-url>[|<key>]"  # base URL verbatim (http ok)
  GADFLY_ALIAS_<NAME>="<majordomo spec>"                  # plain alias / failover chain

Then reference them as "<name>/<model>" (or the bare alias) in GADFLY_MODEL(S).
<NAME> lowercases to the registry name, matching majordomo's LLM_* convention.
LLM_* DSNs still work (and are documented) for HTTPS endpoints. + unit tests,
README "Endpoint aliases via env vars", stub example.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

cmd/gadfly/model_test.go

@@ -2,6 +2,30 @@ package main
 
 import "testing"
 
+func TestEndpointProvider(t *testing.T) {
+	t.Run("ollama http endpoint registers under its name", func(t *testing.T) {
+		p, err := endpointProvider("bigbox", "ollama|http://192.168.1.50:11434")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if p.Name() != "bigbox" {
+			t.Errorf("Name() = %q, want %q", p.Name(), "bigbox")
+		}
+	})
+	t.Run("openai compatible with key", func(t *testing.T) {
+		if _, err := endpointProvider("gpu", "openai|http://gpu.lan:8000/v1|sk-x"); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+	})
+	for _, bad := range []string{"", "ollama", "noprovider-no-pipe", "mystery|http://x"} {
+		t.Run("rejects "+bad, func(t *testing.T) {
+			if _, err := endpointProvider("n", bad); err == nil {
+				t.Errorf("endpointProvider(%q) = nil error, want error", bad)
+			}
+		})
+	}
+}
+
 func TestBuildSpec(t *testing.T) {
 	tests := []struct {
 		name     string